1. Field of the Invention
The present invention relates to a semiconductor fabrication method. More particularly, the present invention relates to a method of fabricating a capacitor.
2. Description of the Related Art
Memory function of a Dynamic Random Access Memory (DRAM) is carried out by controlling the voltage applied to the source region of a metal oxide semiconductor (MOS) transistor. Applying the voltage to the MOS transistor motivates electrons of a capacitor to flow. In this manner, a read or a write operation is carried out. However, when the capacitor is operated, the electrons in the capacitor are in a non-equilibrium state. In this non-equilibrium state, current leakage easily occurs. Therefore, it is necessary to refresh the capacitor periodically.
The refresh frequency depends on the charge-storage ability of the capacitor. As the storage ability of the capacitor increase, the refresh frequency for the capacitor is decreased. Thus, increasing the storage ability of the capacitor has become a development trend.
There are several methods for increasing the storage capacity of the capacitor. The methods include improving dielectric materiel and conductive material, and increasing the surface area of the capacitor. In order to increase the surface area of the capacitor, it is necessary to perform photolithographic, etching, and deposition steps to form a bottom electrode having a certain shape. The deposition methods that are commonly used are chemical vapor deposition and physical vapor deposition. Typically, those deposition methods must be performed at a high temperature. Unfortunately, the high temperature causes a photoresist layer used in a photolithographic and etching step to decompose and contaminate the platform. Therefore, in semiconductor industry, the photoresist layer must be removed before the deposition step. However, this increases the number of fabrication steps needed to form the predetermined capacitor.